Peanut butter or walnut halves. The peanut butter is easier to get to stay on a trap trigger. We had a plague of them (pun intended) on our ranch when I was a kid in the 1950s and my father offered a bounty of 10 cents a squirrel (honor system; we weren't allowed to touch them--CA ground squirrels carry some NASTY diseases. Like the plague.). I started killing them with my .410 but soon found that the smallest Victor traps I could borrow did the job better and cheaper. Then I started using the largest size of rat traps--cheap and effective. I think my Dad finally regretted his bounty.....got pretty expensive for him. Inside the barns I shot many with an old Sheridan .20 air rifle, too.
